Group A: A bolus of remifentanyl 2 µg/kg IBW (0,2 ml/ 10 kg IBW) will be given and followed by 10 - 50 ug/kg IBW/h remifentanyl infusion (1 - 5 ml / 10 kg IBW / h). The propofol and dexmedetomidine infusion will be continued but adapted in dose when needed after the measurements.